The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.
Telecommunications refers to transmission based communication using electromagnetic systems. A telecommunications system typically comprises a network and a plurality of terminals. The network comprises a set of nodes and links that provide connections between two or more terminals to facilitate telecommunication between them.
In addition to networked communications, some terminals are capable of operating in direct mode by using radio frequencies that are not controlled by the network. During direct mode operations, there is a direct connection between the phones. The network may be aware of the direct mode operations but it does not essentially interfere with the procedures of the communication.
In some systems communications between terminals operating under network control and terminals in direct mode are facilitated by means of a gateway. The gateway is a an entity that is able to interface the network and also to participate in the direct mode communications, either via the interface used between direct mode terminals, or via specific direct mode gateway interface.
Typically such a gateway registers to the network using its own address and in most of the communications operations appears to other terminals as one more terminals in the network. In most of these situations this is an excellent arrangement; it facilitates information flows between networked and direct mode operations. The term address represents here identification information and refers to formalized information used to unambiguously indicate an identifiable entity in the network. Addressing a message with particular identification information refers thus here to providing a message with an address, which corresponds with the identification information and using the provided address for routing the message in the network. Address may be provided and used in various forms, depending on the applied network protocols.
However, there are communication situations where the arrangement does not work appropriately. For example, some advanced systems provide a specific mechanism by means of which a terminal in a call may display to its user identification information of the party that is presently talking. This feature is especially valuable in systems that provide group communications, where signalling procedures apply group addresses. For a listener a mere group address is not enough, a user needs to know which one of the group members it is currently listening to.
This talking party identification is practicable and widely used, but it has been noted that the procedure is vulnerable to use of the gateway because the address used for talking party identification is derived from the signalling messages associated to the call. Accordingly, when the talking party is a direct mode terminal that operates via the gateway, the talking party identification displayed by the listening terminal is the address of the gateway, not the address of the talking party. Especially in professional systems this is a severe handicap, because the dispatcher typically operates in the network side. It is very important that the dispatcher knows exactly the party he or she is presently communicating with.
This problem has been noticed in European Telecommunications Standards Institute TETRA system in which a feature called Talking Party Identification (TPI) has been specified. ETSI standards propose solving the problem by configuring the gateway to include the address of a transmitting direct mode terminal (DM-MS) as a type 3 element within a layer 3 protocol data unit (PDU). This type 3 element indicates the source direct mode terminal when the gateway sends a message to the network, or the destination direct mode terminal when the gateway receives a message from the network.
Implementation of the ETSI proposed mechanism, however, requires essential modifications to elements in the side of the network and/or trunked mode terminals. Such modifications require a lot of design and testing work and are therefore expensive to implement. This means that since DM-MS address is an optional feature of the ETSI standards, there has not been many implementations that apply the proposed use of type 3 elements in layer 3 PDUs.
The above situation illustrates the more generic problem of identifying direct mode terminals communicating with network terminals via a gateway that applies the same communication interface as the network terminals. In order to direct the messages to itself in the network the gateway has to use its own address in signalling. If identification information of the direct mode terminal behind the gateway needs to be conveyed to a network terminal, it needs to be delivered within an information element of the signaling message. Signalling messages associated to many communication instances in existing systems are not designed to carry such information elements, and introducing new information elements for existing systems and installed system base is very laborious. And even if such provision had been considered already at the design phase, implementation of a characteristic that is probably not widely used is typically not high in the order of implementations.
However, the need definitely exists and for many important use cases and user populations the disadvantages from not being able to identify a party behind the gateway (typically a person in field operations) are significant. A simple and easy to implement solution is therefore needed to appropriately solve the above problem.